Base station apparatus  and communication method

ABSTRACT

In order to reduce interference between cells through hopping and use frequencies in a good propagation situation, a scheduler section  102  carries out scheduling for determining to which user data should be sent using CQI from each communication terminal apparatus, selects a user signal to be sent in the next frame and determines in which subcarrier block the data should be sent. An MCS decision section  103  selects a modulation scheme and coding method from the CQI of the selected user signal. A subcarrier block selection section  110  selects a subcarrier block instructed by the scheduler section  102  for each user signal. For the respective subcarrier blocks, FH sequence selection sections  111 - 1  to  111 - n  select hopping patterns. A subcarrier mapping section  112  maps the user signal and control data to subcarriers according to the selected hopping pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/550,557 filed Sep. 23,2005, which is a 371 application of PCT/JP2004/004875 filed Apr. 2,2004, which is based on Japanese Application No. 2003-102018 filed Apr.4, 2003, the entire contents of each of which are incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to a base station apparatus andcommunication method, and more particularly, to a base station apparatusand communication method suitable for use in an OFDM scheme.

BACKGROUND ART

OFDM (Orthogonal Frequency Division Multiplexing) is attractingattention as a high-speed transmission technology resistant to multipathinterference. FH-OFDM (Frequency hopping-OFDM) is a scheme whereby OFDMsubcarriers that are used hop around, over time, and is used in, forexample, IEEE802.16, as an access scheme that is capable of achievingfrequency diversity effect(see, for example, “IEEE Standard 802.16: Atechnical overview of the Wireless MAN Air Interface for broadbandwireless access”, pp. 98-107, IEEE Communication Magazine, June, 2002).

Furthermore, FH-OFDM also has an effect of averaging interferencebetween cells in a cellular environment and is drawing attention as afuture high-speed radio transmission technology. Furthermore, the 3GPPis also studying the introduction of FH-OFDM.

In FH-OFDM, base station apparatuses carry out transmission according totheir respective FH patterns. An FH pattern is a pattern related to timetransition and an operating frequency (subcarrier) and each base stationapparatus is assigned a unique FH pattern. The frequency of FH(frequency hopping) may be once every symbol or every slot (or frame).Here, suppose FH for every symbol. Because a frequency is used over awide range, effects of FH include a frequency diversity effect and atemporal averaging effect against interference between cells.

As a method for implementing FH, for example, a method of usingfrequency interleave and a method of using a pattern generated by arandom sequence such as a PN sequence may be available. For simplicity,the latter will be explained here.

Furthermore, for the purpose of channel allocation per cell, there is aproposal to divide a band into subchannels and carry out DCA (DynamicChannel Allocation) in subchannel units (e.g., see “Dynamic channelallocation schemes in mobile radio systems with frequency hopping”,Verdone, R.; Zanella, A.; Zuliani, L., pp. E-157-E-162, vol. 2,Personal, Indoor and Mobile Radio Communications, 2001 12th IEEEInternational Symposium on, September/October 2001).

A conventional base station apparatus and mobile station apparatus willbe explained below. FIG. 1 is a block diagram showing the configurationof a conventional base station apparatus.

In FIG. 1, a scheduler section 11 carries out scheduling using CQI(Channel Quality Indicator) from each mobile station apparatus todetermine to which user data should be sent. There are variousscheduling algorithms such as an MaxC/I method and Round Robin method.Furthermore, a coding method (coding rate) and modulation scheme to beused are determined based on this CQI. A coding section 12 carries outcoding such as turbo coding on user data. Furthermore, the codingsection 12 also carries out processing like interleaving as required.

A transmission HARQ section 13 carries out processing necessary forHARQ. Details will be explained using FIG. 2. FIG. 2 is a block diagramshowing the configuration of a transmission HARQ section of theconventional base station apparatus. As shown in FIG. 2, thetransmission HARQ section 13 is constructed of a buffer 21 and a ratematching section 22. The buffer 21 stores a bit string of transmissiondata. The rate matching section 22 carries out rate matching determinedby an RM parameter on the bit string of the transmission data and inputspunctured or repeated transmission data to a modulation section 14. TheRM parameter may vary depending on a transmission count.

The modulation section 14 modulates the transmission data according toQPSK or QAM. A control data processing section 15 is constructed of acoding section 16 and a modulation section 17. The coding section 16carries out coding on control data. The modulation section 17 modulatesthe control data. A multiplexing section 18 multiplexes (here, timemultiplexing) the transmission data subjected to processing by themodulation section 14 with the control signal which has been likewisesubjected to processing of coding and modulation.

Next, a subcarrier mapping section 19 assigns the transmission data andcontrol signal to subcarriers according to a predetermined FH pattern.Likewise, the subcarrier mapping section 19 also maps pilot signals insuch a way as to be distributed over the entire frequency band. Then,the subcarrier mapping section 19 outputs a transmission signal to whichthe transmission data, control signal and pilot signals are mapped to anS/P conversion section 20.

The S/P conversion section 20 converts the transmission signal fromserial data to parallel data and outputs the parallel data to an IFFTsection 21.

The IFFT section 21 carries out an IFFT (inverse fast Fourier transform)on the transmission signal which has been converted to the paralleldata. A GI insertion section 22 inserts a GI (Guard Interval) into atransmission signal to enhance multipath resistance. A radio processingsection 23 transmits the transmission signal after radio transmissionprocessing.

The state of subcarriers used at this time is as shown in FIG. 3, forexample. FIG. 3 illustrates an example of signals of the conventionalbase station apparatus. In FIG. 3, the vertical axis shows time and thehorizontal axis shows subcarrier frequencies. As shown in FIG. 3,subcarriers carrying pilot signals and data signals vary every timeunit.

In this way, a mobile station apparatus receives signals carried bytime-varying subcarriers on which transmission signals are arranged.FIG. 4 is a block diagram showing the configuration of a conventionalmobile station apparatus.

In FIG. 4, a radio processing section 51 carries out radio receptionprocessing such as down-conversion on a received signal and obtains abaseband signal. A GI elimination section 52 eliminates the inserted GI.An FFT section 53 carries out FFT processing and thereby extracts thesignals of the respective subcarriers. A subcarrier demapping section 54demaps this received signal according to an FH pattern and extracts thesignal assigned to the own station.

Next, a channel separation section 55 separates the received signal intoa user signal, control signal and pilot. A demodulation section 56demodulates the control signal and a decoding section 57 carries outdecoding processing on the control signal subjected to the demodulationprocessing.

A demodulation section 58 demodulates the user signal. A reception HARQsection 59 saves a predetermined number of bits (here, soft decisionbits) after the demodulation of the user signal. In the case ofretransmission, the bits are combined with the reception bits previouslystored. A decoding section 60 carries out decoding on turbo codes, etc.,using the bit string to obtain user data. Here, though not shown, achannel estimation value calculated using pilot signals is used duringdemodulation processing. An ACK/NACK generation section 61 decides basedon a CRC result of the decoded received data whether the received dataincludes errors or not and transmits an ACK signal or NACK signal overan uplink.

Furthermore, a CIR measuring section 62 calculates an average receptionSIR of all subcarriers using pilot signals. A CQI generation section 63generates CQI from the average reception SIR. A transmission section 64transmits the CQI and ACK/NACK signal over the uplink.

However, while the conventional apparatus can achieve a frequencydiversity effect by expanding a band used through frequency hopping,there is a problem that it cannot obtain effects of frequency schedulingwhereby transmission is performed using frequencies in a goodpropagation path situation. Furthermore, since the frequency hoppingrange of the conventional apparatus extends over a wide band, an amountof control information becomes enormous when hopping patterns areassigned to the respective users as channel resources.

Furthermore, according to conventional frequency scheduling wherebypackets are transmitted using frequencies of good reception quality,when a base station apparatus in an adjacent cell also assigns the samefrequency to other mobile station apparatuses, it may not be possible toreceive packets due to interference.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a base stationapparatus and communication method capable of reducing interferencebetween cells through hopping, using frequencies in a good propagationsituation, realizing high-speed transmission and reducing an amount ofcontrol information on resource assignment.

In order to achieve the above described object, the present inventiondivides a communication frequency band into subcarrier blocks, selects asubcarrier block to be used in a frame through frequency scheduling andcauses each user signal to be subjected to frequency hopping within theselected block. Through this hopping, it is possible to reduceinterference between cells and use frequencies in a good propagationsituation. As a result, it is possible to realize faster transmission.

Thus, the present invention is intended to enhance the frequencyscheduling effect by narrowing the hopping range and particularlyeffective in an environment with a large number of users and large delayvariance. Furthermore, the present invention can reduce the number ofpatterns of frequency hopping by dividing a band into subcarrier blocksand reduce an amount of control information for resource assignment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionalbase station apparatus;

FIG. 2 is a block diagram showing the configuration of a transmissionHARQ section of the conventional base station apparatus;

FIG. 3 illustrates an example of signals of the conventional basestation apparatus;

FIG. 4 is a block diagram showing the configuration of a conventionalmobile station apparatus;

FIG. 5 illustrates a block diagram showing the configuration of a basestation apparatus according to Embodiment 1 of the present invention;

FIG. 6 illustrates an example of subcarrier mapping of the base stationapparatus according to Embodiment 1 of the present invention;

FIG. 7 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram showing the configuration of a CIR measuringsection of the communication terminal apparatus according to Embodiment1 of the present invention;

FIG. 9 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention;

FIG. 10 illustrates an example of subcarrier mapping of the base stationapparatus according to Embodiment 2 of the present invention;

FIG. 11 illustrates the configuration of a CIR measuring section of abase station apparatus according to Embodiment 3 of the presentinvention;

FIG. 12 illustrates an example of fading variation according toEmbodiment 4 of the present invention;

FIG. 13 illustrates an example of fading variation according toEmbodiment 4 of the present invention;

FIG. 14 illustrates a concept of Embodiment 4 of the present invention;and

FIG. 15 is a block diagram showing the configuration of a base stationapparatus and control station apparatus according to Embodiment 4 of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below.

Embodiment 1

This embodiment will explain a case with transmission using FH-OFDMwhere an operating frequency band is divided into subcarrier blocks anda base station apparatus selects a subcarrier block to be used in aframe for each user through frequency scheduling. Each user signal issubjected to frequency hopping within the block. With an operatingfrequency band divided into subcarrier blocks, it is possible to assigna frequency to a most suitable user. Furthermore, causing the operatingsubcarriers to hop within a block can reduce interference between cells.

FIG. 5 illustrates a block diagram showing the configuration of a basestation apparatus according to Embodiment 1 of the present invention.The base station apparatus 100 in FIG. 5 is mainly constructed of areception section 101, a scheduler section 102, an MCS decision section103, a coding section 104-1, a coding section 104-2, a transmission HARQsection 105-1, a transmission HARQ section 105-2, a modulation section106-1, modulation section 106-2, a control data processing section 107,a coding section 108, a modulation section 109, a subcarrier blockselection section 110, FH sequence selection sections 111-1 to 111-n, asubcarrier mapping section 112, an S/P conversion section 113, an IFFTsection 114, a GI insertion section 115 and a radio processing section116.

In FIG. 5, the reception section 101 receives a received signaltransmitted from a communication terminal apparatus which is the otherparty of communication, converts the frequency of this received signalto a baseband signal, decodes the baseband signal and extracts CQI. Thereception section 101 outputs the CQI to the scheduler section 102 andMCS decision section 103.

The scheduler section 102 carries out scheduling of deciding to whichuser data should be transmitted using CQI from each communicationterminal apparatus and selects a user signal to be transmitted in thenext frame. As the scheduling method, algorithms such as MaxC/I methodand Round Robin method are available. At this time, the schedulersection 102 also decides in which subcarrier block the user data shouldbe transmitted and outputs the information to the subcarrier blockselection section 110. Here, the scheduler section 102 selects asubcarrier block in an optimum propagation path.

The MCS decision section 103 selects a modulation scheme and codingmethod (coding rate) from the CQI of the selected user signal, outputsthe coding scheme to the coding section 104-1 and coding section 104-2and outputs the modulation scheme to the modulation sections 106-1 and106-2.

The coding section 104-1 and coding section 104-2 carry out coding onuser data through turbo coding, etc., according to a coding schemeinstructed by the MCS decision section 103. Furthermore, the codingsection 104-1 and coding section 104-2 also carry out processing such asinterleaving as required. The coding section 104-1 and coding section104-2 output the coded user data to the transmission HARQ section 105-1and transmission HARQ section 105-2.

The transmission HARQ section 105-1 and transmission HARQ section 105-2save the coded user data in an HARQ buffer and carry out rate matchingprocessing of the coded user data according to a retransmission count.The coded user data is output to the modulation section 106-1 andmodulation section 106-2.

The modulation section 106-1 and modulation section 106-2 modulate theuser data according to the modulation scheme instructed by the MCSdecision section 103 and output the modulated signal to the subcarrierblock selection section 110.

The control data processing section 107 is constructed of the codingsection 108 and modulation section 109. The coding section 108 carriesout coding on the control data and outputs the control data to themodulation section 109. The modulation section 109 modulates the controldata and outputs the modulated control data to the subcarrier blockselection section 110.

The subcarrier block selection section 110 assigns subcarrier blocksinstructed by the scheduler section 102 to their respective usersignals. The FH sequence selection sections 111-1 to 111-n selecthopping patterns for the respective subcarrier blocks.

For control data such as subcarrier block assignment information and MCSinformation, predetermined subcarrier blocks and FH sequences areselected. Therefore, the subcarrier block selection section 110 selectsuser signals that differ from the FH sequences of the control data.

Then, the subcarrier mapping section 112 maps the user signals andcontrol data to subcarriers according to the selected hopping patterns.An example of mapping at this time is shown in FIG. 6. FIG. 6 shows anexample of mapping of the subcarriers of the base station apparatus ofthis embodiment.

In FIG. 6, the horizontal axis shows subcarrier frequencies and thevertical axis shows time in frame units. As shown in FIG. 6, signals aresubjected to frequency hopping in subcarrier block units. Subcarrierblocks for signal mapping are then determined for every frame. For thesubcarrier blocks for signal mapping, subcarrier blocks whosepropagation path quality is equal to or higher than predeterminedquality are selected for every frame. Furthermore, though not shown,pilot signals are also mapped simultaneously.

The S/P conversion section 113 converts the mapped signal from serialdata to parallel data and outputs the parallel data to the IFFT section114. The IFFT section 114 subjects the transmission signal converted tothe parallel data to IFFT (inverse fast Fourier transform). The GIinsertion section 115 inserts a GI (Guard Interval) into thetransmission signal to enhance multipath resistance. The radioprocessing section 116 converts the transmission signal to a radiofrequency and transmits the signal.

Thus, according to the base station apparatus of this embodiment, a bandis divided into subcarrier blocks, subcarrier blocks used are selectedfor every frame through frequency scheduling and each user signal issubjected to frequency hopping within the block. Through such hopping,it is possible to use frequencies in a good propagation situation whilereducing interference between cells and transmit data at a high speed.Furthermore, it is possible to reduce the number of patterns offrequency hopping by dividing the band into subcarrier blocks and reducean amount of control information for resource assignment.

Next, a communication terminal apparatus which communicates with thebase station apparatus 100 will be explained. FIG. 7 is a block diagramshowing the configuration of the communication terminal apparatusaccording to this embodiment. The communication terminal apparatus 200in FIG. 7 is mainly constructed of a radio processing section 201, a GIelimination section 202, an FFT section 203, a subcarrier blockextraction section 204, data sequence reproduction sections 205-1 and205-2, demodulation sections 206-1 and 206-2, a decoding section 207, areception HARQ section 208, a decoding section 209, an ACK/NACKgeneration section 210, a pilot signal extraction section 211, a CIRmeasuring section 212, a CQI generation section 213 and a transmissionsection 214.

In FIG. 7, the radio processing section 201 down-converts the receivedsignal to a baseband signal and outputs the baseband signal to the GIelimination section 202. The GI elimination section 202 eliminates a GIfrom the received signal and outputs the received signal to the FFTsection 203. The FFT section 203 transforms the received signal to afrequency domain through a fast Fourier transform and outputs thetransformed signal to the subcarrier block extraction section 204.

The subcarrier block extraction section 204 separates the receivedsignal into subcarrier blocks and outputs those blocks to the datasequence reproduction sections 205-1 and 205-2. The data sequencereproduction sections 205-1 and 205-2 carry out processing of restoringeach data sequence which has been subjected to hopping to its originalstate. This processing is carried out using subcarrier block assignmentinformation and FU sequence assignment information included in thecontrol data. The data sequence reproduction section 205-1 outputs theprocessed received signal (control data) to the demodulation section206-1. On the other hand, the data sequence reproduction section 205-2outputs the processed received signal (user data) to the demodulationsection 206-2.

The demodulation section 206-1 demodulates the received signal andoutputs the demodulated signal to the decoding section 207. Thedemodulation section 206-2 demodulates the received signal and outputsthe demodulated signal to the HARQ section 208.

The decoding section 207 decodes the demodulated received signal.

The decoding section 207 outputs the subcarrier block assignmentinformation included in the received signal to the subcarrier blockextraction section 204 and outputs the FH sequence assignmentinformation to the data sequence reproduction section 205-1 and datasequence reproduction section 205-2.

The reception HARQ section 208 combines the received signal withprevious received data using a reception HARQ at the time ofretransmission, saves data for new data and outputs the processedreceived signal to the decoding section 209. The decoding section 209demodulates and decodes received signals to obtain user data.Furthermore, the decoding section 209 outputs CRC (Cycle RedundancyCheck) information of the decoded user data to the ACK/NACK generationsection 210.

The ACK/NACK generation section 210 generates an ACK signal or a NACKsignal indicating whether user data has been received correctly or notand outputs the ACK signal or the NACK signal to the transmissionsection 214.

Here, subcarrier blocks and FH sequences to be used for the control dataare predetermined, and therefore the control data is decoded first andthen the user data is processed. Furthermore, the pilot signalextraction section 211 extracts pilot signals included in the respectiveblocks extracted by the subcarrier block extraction section 204 andoutputs the pilot signals to the CIR measuring section 212. The CIRmeasuring section 212 measures a CIR for each subcarrier block. Whatshould be measured as indicative of reception quality are not limited tothe CIR but can also be reception power.

The CQI generation section 213 generates a CQI from the CIR and outputsthe CQI signal to the transmission section 214. The transmission section214 modulates an ACK signal or NACK signal and CQI signal and convertstheir frequencies and transmits the signals as radio signals.

Next, the internal configuration of the CIR measuring section 212 willbe explained. FIG. 8 is a block diagram showing the configuration of theCIR measuring section of the communication terminal apparatus accordingto this embodiment.

Signal power calculation sections 301-1 to 301-3 calculate power valuesof desired signals of the respective subcarrier blocks and output thepower values to CIR calculation sections 303-1 to 303-3.

Interference power calculation sections 302-1 to 302-3 calculate powervalues of interference signals of the respective subcarrier blocks andoutput the power values to the CIR calculation section 303-1 to 303-3.

The CIR calculation sections 303-1 to 303-3 calculate the ratio of adesired signal to an interference signal and output the ratio to the CQIgeneration section 213.

Thus, according to the communication terminal apparatus of thisembodiment, received signals subjected to frequency hopping are restoredto original signals in subcarrier block units. Through such hopping, itis possible to reduce interference between cells, use frequencies in agood propagation situation and realize high-speed transmission.

Note that the transmission HARQ sections 105-1,105-2 and reception HARQsection 208 in the above explanations may be omitted. Furthermore, acase where a communication is carried out with a fixed MCS can also beconsidered.

Embodiment 2

FIG. 9 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention. However,those having the same configurations as those in FIG. 5 are assigned thesame reference numerals as those in FIG. 5 and detailed explanationsthereof will be omitted.

The base station apparatus 400 in FIG. 9 differs from the base stationapparatus in FIG. 5 in that it is provided with a control dataprocessing section 401, a subcarrier block selection section 402 and asubcarrier block hopping sequence generation section 403 and subcarrierblocks are subjected to hopping also for a control channel and a channelwhich sequentially transmits speech, etc., at a low rate. The controldata processing section 401 is mainly constructed of a coding section411 and a modulation section 412.

In FIG. 9, the coding section 411 carries out coding on control data,speech data, broadcast signal and multicast signal and outputs the codedsignals to the modulation section 412. The modulation section 412modulates the control data, speech data, broadcast signal and multicastsignal and outputs the modulated signals to the subcarrier blockselection section 402.

The subcarrier block selection section 402 assigns subcarrier blocksinstructed by a scheduler section 102 to the respective user signals.For the respective subcarrier blocks, hopping patterns are selected byFH sequence selection sections 111-1 to 111-n.

Furthermore, the subcarrier block selection section 402 receives ahopping sequence of subcarrier blocks from the subcarrier block hoppingsequence generation section 403. The subcarrier block selection section402 assigns subcarrier blocks to the control data, speech data,broadcast signal and multicast signal output from the modulation section412 according to this hopping sequence. For these subcarrier blocks, theFH sequence selection sections 111-1 to 111-n also select hoppingpatterns as in the case of user signals.

The subcarrier block hopping sequence generation section 403 generates asequence (pattern) for causing the subcarrier blocks to which controldata is mapped to hop around, over time. Here, a predetermined sequenceis generated for each base station. The subcarrier block hoppingsequence generation section 403 instructs the subcarrier block selectionsection 402 on the subcarrier blocks to be assigned to the control datain current transmission units according to the sequence generated.

FIG. 10 illustrates an example of subcarrier mapping of the base stationapparatus of this embodiment. In FIG. 10, the horizontal axis showssubcarrier frequencies and the vertical axis shows time in frame units.

As shown in FIG. 10, the control data (in addition, speech data,broadcast signal and multicast signal) are subjected to frequencyhopping in subcarrier block units. The subcarrier blocks for signalmapping are determined for every frame.

Thus, the base station apparatus according to this embodiment alsosubjects subcarrier blocks to hopping for control channels and channelsfor sequentially transmitting speech, etc., at a low rate, and thereforeit is possible to obtain a frequency diversity effect, obtain uniformand stable reception quality and improve speech quality.

Furthermore, when carrying out transmission using scheduling forlow-rate signals, the ratio of control signals in the signal amount(ratio of overhead) increases, which is not efficient. However, it ispossible to realize efficient transmission by carrying out hopping ofsuch subcarrier blocks.

Furthermore, broadcast information, multicast information and subcarrierblocks used for news delivery are also subjected to hopping. Thisimproves reception quality for information transmitted to many usersthrough a frequency diversity effect.

Embodiment 3

Users on a cell boundary receive strong interference from adjacentcells. Since users in other cells do not know to which subcarrier blocksthey are assigned next and the users cannot predict an amount ofinterference. Therefore, for the users on a cell boundary, theirsubcarrier blocks may receive a small amount of interference and have ahigh CIR at an actual moment but may have a greater amount ofinterference next moment. When measuring a CIR as the reception qualityfeed back by a communication terminal apparatus, this embodiment uses ameasured value for each block as signal power (C) and uses an averagevalue of interference power of respective blocks as interference power(I).

FIG. 11 illustrates the configuration a CIR measuring section of thebase station apparatus according to Embodiment 3 of the presentinvention. However, components having the same configurations as thosein FIG. 8 are assigned the same reference numerals as those in FIG. 8and explanations thereof will be omitted. The CIR measuring section inFIG. 11 is different from the CIR measuring section in FIG. 8 in that itis provided with an interference power averaging section 601, CIRcalculation sections 602-1 to 602-3, calculates an average value ofinterference power and calculates a CIR from this average value.

Signal power calculation sections 301-1 to 301-3 calculate power valuesof desired signals of the respective subcarrier blocks and output thepower values to the CIR calculation sections 602-1 to 602-3.

Interference power calculation sections 302-1 to 302-3 calculate powervalues of interference signals of the respective subcarrier blocks andoutput the power values to the interference power averaging section 601.

The interference power averaging section 601 calculates an average valueof the power of interference signals calculated by the interferencepower calculation sections 302-1 to 302-3 and outputs the average valueto the CIR calculation sections 602-1 to 602-3.

The CIR calculation sections 602-1 to 602-3 calculate a ratio of thepower value of a desired signal for each subcarrier block to the averagepower value of an interference signal and output the ratio to the CQIgeneration section 213.

Thus, the communication terminal apparatus according to this embodimentmeasures interference power for each subcarrier block, calculates anaverage value of interference power of a plurality of subcarrier blocksand calculates a ratio of the power value of a desired signal of eachsubcarrier block to the average value of interference power as a CIR.This makes it possible to reduce influences of unpredictable variationsof interference, measure more accurate channel reception quality, andthereby allow a base station apparatus to select more suitablesubcarrier blocks and improve throughput. This also leads to a selectionof an optimal MCS.

Embodiment 4

Embodiment 4 will explain an example where the size of a subcarrierblock is made variable for each cell.

In general, cells having a small radius are arranged in urban areasbecause there is a high user density, while cells having a large radiusare arranged in suburbs. Delay variance is small (1 μs or less) in thecase of a small cell, while delay variance is large (5 μs or above) inthe case of a large cell.

FIG. 12 and FIG. 13 show examples of a fading variation. In FIG. 12 andFIG. 13, the horizontal axis shows a frequency used for a communicationand the vertical axis shows the magnitude of fading variation.

FIG. 12 is an example where delay variance is large. As shown in FIG.12, when there is large delay variance, fading in the frequencydirection changes drastically, and reception power changes withinsubcarrier blocks unless the sizes of the subcarrier blocks are reduced,which makes it impossible to assign optimum subcarriers according toreception quality of the respective users. Furthermore, it is a generalpractice to decide an MCS from a CIR on the premise that the receptionquality is substantially constant, but when a fading variation is largewithin a block, the accuracy of MCS selection also deteriorates.

FIG. 13 shows an example where delay variance is small. As shown in FIG.13, when delay variance is small, a fading variation in the frequencydirection is small, and therefore there is no problem even if the sizeof a subcarrier block is relatively large. On the other hand, when thesize of the subcarrier block is too small, the amount of control signalsuch as report on the reception quality of subcarrier blocks anddownlink assignment information increases. From the tradeoff betweenthem, it is imaginable that there exist optimum values in the sizes ofsubcarrier blocks according to the radius of the cell.

Therefore, Embodiment 4 makes the block size variable for each cell andsets a value corresponding to the cell size. FIG. 14 illustrates theconcept of Embodiment 4 of the present invention. Suppose cell A at topleft and cell B at bottom left are small cells and cell C at top rightis a large cell. For cell A and cell B, each block size is increased and4 blocks are set. For cell C, each block size is reduced and a total of8 blocks are set. A control station 701 notifies base stationapparatuses 702, 703 and 704 of the block sizes of the respective cells.The control station 701 notifies this to the base station apparatuses702, 703 and 704 as annunciation information. Each cell carries outprocessing according to Embodiments 1 to 3 in the respective block sizesnotified.

Here, when a comparison is made with respect to the amount of controlsignal, there is a CQI (e.g., 6 bits) of each subcarrier block measuredby a communication terminal apparatus on the uplink. Since cells A, Brequire CQIs for 4 blocks, only 24 bits are required, but cell Crequires 48 bits.

On the downlink, there is information as to which subcarrier blockshould be used. Since cells A, B require the information for 4 blocks,only 4 bits are required, but cell C requires the information for 8blocks, and so it requires 8 bits. (In the case where a plurality ofsubcarrier blocks can be assigned)

Furthermore, it is necessary to send an MCS (e.g., 6bits) of eachsubcarrier block. For cells A, B, only 4×6=24 bits are required, whilecell C requires 8×6=48 bits. Though the amount of control informationincreases in cell C, high accuracy control according to a fadingvariation in the frequency direction is available.

Next, the inner configuration of the base station apparatus of thisembodiment will be explained. FIG. 15 is a block diagram showing theconfigurations of the base station apparatus and control stationapparatus according to this embodiment. However, the components havingthe same configurations as those in FIG. 5 are assigned the samereference numerals as those in FIG. 5 and detailed explanations thereofwill be omitted.

The base station apparatus 800 in FIG. 15 is different from the basestation apparatus in FIG. 5 in that it is provided with a receptionsection 801, a delay variance calculation section 802 and a block sizeinformation reception section 803 and selects small blocks when delayvariance in a propagation path is large and selects large blocks whendelay variance is small. Furthermore, the control station apparatus 850in FIG. 15 is mainly constructed of a delay information receptionsection 851, a block size determining section 852 and a transmissionsection 853.

The reception section 801 receives a signal sent from a communicationterminal apparatus which is the other party of communication, convertsthe frequency of this received signal to a baseband signal, decodes thebaseband signal and extracts CQI. The reception section 801 outputs theCQI to a scheduler section 804 and an MCS decision section 103.Furthermore, the reception section 801 also outputs the received signalto the delay variance calculation section 802.

The delay variance calculation section 802 calculates the magnitude ofdelay variance of the propagation path from the received signal andoutputs it to the delay information reception section 851.

The delay information reception section 851 receives information on thedelay variance output from the base station apparatus 800 and outputsthe information to the block size determining section 852. Note that theinformation on the delay variance received is information on the delayvariance output from a plurality of base station apparatuses as shown inFIG. 14.

The block size determining section 852 selects small blocks for a cellhaving large delay variance in the propagation path based on theinformation on the delay variance output from a plurality of basestations and selects large blocks for a cell having small delayvariance. Here, a small block indicates a subcarrier block having asmall number of subcarriers and a large block indicates a subcarrierblock having a large number of subcarriers.

The transmission section 853 outputs information on the block sizedetermined by the block size determining section 852 to the block sizeinformation reception section 803 of each base station apparatus.

The block size information reception section 803 outputs the receivedinformation on the block size to the scheduler section 804 andsubcarrier block selection section 805.

The scheduler section 804 carries out scheduling for determining towhich user data should be sent using CQI from each communicationterminal apparatus and selects a user signal to be sent in the nextframe. As the scheduling method, algorithms such as MaxC/I method andRound Robin method are available. At this time, the scheduler section804 also determines in which subcarrier block of the subcarrier blocksin the block size determined by the block size determining section 852transmission is performed and outputs the information to the subcarrierblock selection section 805. Here, the scheduler section 804 selects asubcarrier block in the best propagation path.

The subcarrier block selection section 805 selects subcarrier blocksinstructed from the scheduler section 804 out of the subcarrier blocksin the block size determined by the block size determining section 852for the respective user signals. Furthermore, FH sequence selectionsections 111-1 to 111-n select hopping patterns for the respectivesubcarrier blocks.

Thus, according to the control station apparatus and base stationapparatus of this embodiment, it is possible to reduce the amount ofcontrol signal by selecting small blocks for a cell having large delayvariance in the propagation path and large blocks for a cell havingsmall delay variance.

Note that the control station apparatus and base station apparatusaccording to this embodiment is applicable not only to an FH-OFDM schemebut also to other multicarrier communication schemes. Furthermore, it isalso possible to integrate the control station apparatus and basestation apparatus and determine block sizes using delay variance of onebase station apparatus.

The present invention is not limited to the above described embodimentsand can be implemented modified in various ways. For example, the abovedescribed embodiments have explained the case where the invention isimplemented as a base station apparatus, but instead of this, thiscommunication method can also be implemented by software.

For example, it is possible to store a program for executing the abovedescribed communication method in a ROM (Read Only Memory) beforehandand cause a CPU (Central Processor Unit) to operate the program.

Furthermore, it is also possible to store a program for implementing theabove described communication method in a computer-readable storagemedium, record the program stored in the storage medium in a RAM (RandomAccess Memory) of a computer and cause the computer to operate accordingto the program.

Thus, the present invention divides a band into subcarrier blocks,selects subcarrier blocks used in frame units through frequencyscheduling, subject respective user signals to frequency hopping withinthe blocks, and can thereby reduce interference between cells throughhopping, use frequencies in good propagation situations and realizehigh-speed transmission. Furthermore, the invention divides the band,and can thereby reduce the number of patterns of frequency hopping andreduce the amount of control information on resource assignment to therespective users.

Furthermore, the invention also subjects subcarrier blocks to hoppingand obtains a frequency diversity effect, and can thereby obtain uniformand stable reception quality for a control channel and channels such asspeech requiring uniform quality at a low rate and realize stablecommunications.

Furthermore, by restoring a received signal subjected to frequencyhopping to the original signal in subcarrier block units, it is possibleto reduce interference between cells through hopping, use frequencies ina good propagation situation and realize high-speed transmission.

Furthermore, by measuring interference power for every subcarrier block,calculating an average value of interference power of a plurality ofsubcarrier blocks and calculating the ratio of a power value of adesired signal of each subcarrier block to an average value ofinterference power as a CIR, it is possible to reduce influences ofunpredictable variation of interference and measure more accuratechannel reception quality and thereby allow the base station apparatusto select more suitable subcarrier blocks, which improves throughput andalso leads to a selection of a more suitable MCS.

As explained so far, the present invention can reduce interferencebetween cells and realize high-speed transmission using frequencies in agood propagation situation.

This application is based on the Japanese Patent Application No.2003-102018 filed on Apr. 4, 2003, entire content of which is expresslyincorporated by reference herein.

1. A base station apparatus comprising: a mapping unit that maps controldata to a predetermined block among a plurality of blocks into which afrequency band is divided, and that maps user data to a block selectedfrom the plurality of the blocks; and a transmitting unit that transmitsthe control data mapped to the predetermined block and the user datamapped to the selected block, wherein: said mapping unit maps thecontrol data such that the control data are distributed within thepredetermined block.
 2. The base station apparatus according to claim 1,further comprising a frequency hopping unit that performs frequencyhopping of the user data within the selected block.
 3. A communicationmethod comprising: mapping control data to a predetermined block among aplurality of blocks, into which a frequency band is divided, such thatthe control data are distributed within the predetermined block; mappinguser data to a block selected from the plurality of the blocks; andtransmitting the control data mapped to the predetermined block and theuser data mapped to the selected block.
 4. The communication methodaccording to claim 3, further comprising frequency-hopping the user datawithin the selected block.